Magnetic-based indicator tools are used to determine a setting of an implantable medical device. The implantable medical device may include a fluid flow control valve that controls the pressure of cerebral spinal fluid (CSF) in a patient's brain. Excessive accumulation of cerebral spinal fluid (CSF), due to hydrocephalus or other causes, manifests itself as increased pressure within the brain. Relieving the CSF pressure is therapeutically beneficial and is usually done by using a fluid flow control valve to drain CSF from ventricles in the brain.
The implantable medical device may include a target in the form of a magnet. The magnet allows a tool set to determine the setting of the medical device and change the setting without removing the subcutaneously implanted device. The tool set typically includes a locator tool to determine the orientation of the medical device, the magnetic-based indicator tool to determine the setting of the implantable medical device by using a compass, and an adjustment tool to change the setting of the medical device by using another magnet. The tool set works by using magnetic coupling between the magnet on the implantable medical device and each of the indicator tool compass and the adjustment tool magnet.
Prior magnetic-based indicator tool relies on an interaction between the magnet on the medical device and a compass on the indicator tool that is strong enough to determine the position of the magnet even through a patient's scalp. The magnet-compass interaction must also be resistant to external magnetic fields, especially from the earth. The compass will drift toward aligning with the earth's magnetic field if the pull of the magnet in the implanted medical device is not strong enough. The deflection angle increases as the distance between the magnet and the compass increases, and may lead to inaccurate device setting indications.
Alternatively, magnetic based location tools have been developed to determine the three-dimensional location of magnetic devices within implanted medical devices. These alternate location systems typically do not attempt to determine the orientation of the magnetic devices in question and do not relate to the rotatable orientation of devices that are part of implantable valve devices. In addition, magnetic based location tools that are capable of determining the location and orientation of implanted magnetic devices are significantly more complicated in the operations performed than compass-based tools, and as such, are significantly more expensive.
U.S. Published Patent Application No. 2002/0022793 to Bertrand et al. discloses a compass-based indicator for assessing the position of a fluid flow valve within an implanted device. The fluid flow valve described by Bertrand et al. may be used for controlling the flow of cerebral spinal fluid (CSF) in a patient with hydrocephalus. This compass-based indicator is used in combination with an implantable flow control device disclosed within U.S. Pat. No. 5,637,083 to Bertrand et al. U.S. Pat. No. 5,879,297 and U.S. Pat. No. 6,129,668 to Haynor et al. discloses an electronic device to determine the location of a magnet coupled to an indwelling medical device using a plurality of magnetic sensors. Table 1 below lists documents that disclose devices for determining the location and orientation of magnetic devices within implantable medical devices.
TABLE 1U.S. Pat. No.InventorsTitleU.S. 5,637,083Bertrand et al.Implantable Adjustable Fluid Flow Control Valve2002/0022793Bertrand et al.Tool for adjusting an implantable adjustable fluid flow control valveU.S. 5,879,297Haynor et al.System and method to determine the location and orientation of an indwelling medical deviceU.S. 6,129,668Haynor et al.System and method to determine the location and orientation of an indwelling medical device
All documents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and Claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the structures and techniques of the present invention.
An example of a fluid control device is shown in U.S. Pat. No. 5,637,083 issued to William J. Bertrand and David A. Watson on Jun. 10, 1997 entitled “Implantable Adjustable Fluid Flow Control Valve,” the teaching of which is incorporated herein in its entirety by reference. The valve of the '083 patent is shown in FIGS. 1-2 generally labeled 10 (20). (Reference numbers in parentheses correspond to the reference numbers in the '083 patent. After the corresponding reference number to the '083 patent has been given once, no further reference to the '083 will be given although the connection to the '083 patent is intended to be implied throughout this description.) The valve 10 includes an inlet connector 12 (22) and an outlet connector 14 (24). An elastomeric casing 16 (30) covers the inner workings of the valve 10. A dome 18 (60) extends upward from the elastomeric casing 16. Fluid flows through the valve 10 in the direction indicated by the arrow “A.”
Valve 10 includes a mechanism to control fluid flow through the valve 10. The mechanism includes a magnet 20 (120) embedded within a base 22 (122). Rotating the base 22 changes the internal configuration of the mechanism. Changing the internal configuration of the mechanism produces a variety of pressure or flow characteristics for the valve. The base 22 may be rotated by magnetically coupling an external magnet 24 (140) to the valve's magnet 20 and rotating the external magnet 24. Because magnet 20 is coupled to the external magnet 24, when magnet 24 rotates, magnet 20 also rotates. As magnet 20 rotates, base 22 rotates and the internal configuration of the mechanism changes as described in detail in the '083 patent. As the internal configuration of the valve 10 changes, the pressure/flow characteristics of the valve 10 change. In use, the valve 10 is subcutaneously placed on the patient's skull. The catheter going to the patient's ventricle is attached to inlet connector 12. The catheter going to the patient's peritoneal cavity or vascular system is attached to outlet connector 14. In this way, a direction of flow is established from the inlet connector 12 through the valve 10 to the outlet connector 14. As stated above and described in detail in the '083 patent, changing the internal configuration of the mechanism by coupling the external magnet to the internal magnet and rotating the base produces a variety of pressure or flow characteristics through the valve 10.